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Min J.,Structural Engineering Research Institute | Shim H.,National Science Foundation | Yun C.-B.,Korea Advanced Institute of Science and Technology | Hong J.-W.,Korea Advanced Institute of Science and Technology
Smart Structures and Systems | Year: 2016

We propose an effectivemethodology using electromechanical impedance characteristics for estimating theremaining tensile force oftendonsand simultaneously detecting damages of the anchorage blocks. Onceone piezoelectric patchis attached on the anchor head and the other is bonded on the bearing plate, impedance responses are measured through these two patchesunder varying tensile force conditions. Then statistical indices are calculated from the impedances, and two types of relationship curves between the tensile force and the statistical index (TE Curve) and between statistical indices of two patches (SR Curve)are established. Thoseare considered as database for monitoring both the tendon and the anchorage system.Ifdamage exists on the bearing plate, the statistical index of patchon the bearing plate wouldbe out of bounds of the SR curve and damage can be detected. A change in the statistical index bydamage is calibrated with the SR curve, and the tensile force can be estimated with the corrected index and the TE Curve. For validation of the developed methodology, experimental studies areperformed on thescaled model of an anchorage systemthat is simplified only with 3 solid wedges, a 3-hole anchor head, and a bearing plate. Then, the methodology is applied to a real scale anchorage system that has 19 strands, wedges, an anchor head, a bearing plate, and a steel duct.It is observed that the proposed scheme gives quite accurate estimation of the remaining tensile forces. Therefore, this methodology has great potential forpractical useto evaluate the remaining tensile forces and damage status in the post-tensioned structural members. © Copyright 2016 Techno-Press, Ltd.

Lee H.-S.,Hanyang University | Jang H.-O.,Hanyang University | Cho K.-H.,Structural Engineering Research Institute
Materials | Year: 2016

This study set out to derive the optimal conditions for ensuring the monolithicity of ultra-high-performance concrete (UHPC). Direct shear tests were performed to examine the influence on the bonding shear performance. The experimental variables included tamping and delay, which were set to 0, 15, 30, and 60 min. SEM and XRD analyses of the microstructure and composition were performed. The direct shear tests showed that the bonding shear strength was enhanced by the addition of tamping. For the normal-strength concrete (NSC), it is thought that a monolithicity of around 95% can be attained with a cold joint formation delay up to 60 min. In contrast, while the normalized bonding shear strength reduction of UHPC with a delay of 15 min was the lowest at around 8%, a dramatic degradation in the bonding shear performance was observed after 15 min. XRD analyses of the middle and surface sections revealed the composition of the thin film formed at the surface of the UHPC and, as a result, the main component appeared to be SiO2, which is believed to be a result of the rising of the SiO2-based filler, used as an admixture in this study, towards the surface, due to its low specific gravity. © 2016 by the authors.

Heo S.,Inha University | Koo W.,Inha University | Park M.-S.,Structural Engineering Research Institute
International Journal of Structural Stability and Dynamics | Year: 2016

A fast, reliable and optimized numerical procedure of the hydrodynamic response analysis of a slender-body structure is presented. With this method, the dynamic response and reliability of a six-leg jack-up-type wind turbine installation vessel under various environmental conditions is analyzed. The modified Morison equation is used to calculate the wave and wind-driven current excitation forces on the slender-body members. The Det Norske Veritas (DNV) rule-based formula is used to calculate the wind loads acting on the superstructure of the jack-up leg. From the modal analysis, the natural period and standardized displacement of the structure are determined. The Newmark-beta time-integration method is used to solve the equation of motion generating the time-varying dynamic responses of the structure. A parametric study is carried out for various current velocities and wind speeds. In addition, a reliability analysis is conducted to predict the effects of uncertainty of the wave period and wave height on the safety of structural design, using the reliability index to indicate the reliability of the dynamic response on the critical structural members. © 2016 World Scientific Publishing Company

Lee C.-H.,Research Institute of Structural Engineering and System | Ju Y.K.,Korea University | Min J.-K.,Built Environment Materials Center | Lho S.-H.,Structural Engineering Research Institute | Kim S.-D.,Korea University
Engineering Structures | Year: 2015

This paper describes the cyclic performance of non-uniform steel strip dampers. The shapes proposed are (a) a dumbbell-shaped strip, (b) a tapered strip, and (c) an hourglass-shaped strip. Each of these strip shapes was designed to reduce stress concentration when subjected to cyclic loadings. In order to evaluate the performance of the dampers, six specimens were tested cyclically. Cumulative damage caused by hysteretic motion was effectively distributed throughout the entire height of the strips, and SEM microstructures of the fracture surfaces represented a typical ductile failure mode. The experimental results showed that the proposed strip dampers indicate excellent seismic performance compared to conventional prismatic slit dampers. Furthermore, it was verified that structural performance can be accurately estimated using the design equations presented in the paper. © 2015 Elsevier Ltd.

You Y.-J.,Yonsei University | You Y.-J.,Structural Engineering Research Institute | Kim J.-H.J.,Yonsei University | Park Y.-H.,Structural Engineering Research Institute | Choi J.-H.,Yonsei University
Journal of Advanced Concrete Technology | Year: 2015

Glass fiber reinforced polymer (GFRP) has been proposed to replace steel as a reinforcing bar (rebar) material due to its high specific tensile strength and non-corrosive material property. Various GFRP rebars and design guidelines were developed in the past. However, the usage of the rebars has not been widespread in the construction industry due to various restrictions (e.g., lack of standardized shape, lack of confidence in long-term performance of GFRP reinforced concrete (RC) members, and lack of price competitiveness over conventional steel rebar). In this study, the applicability of GFRP rebars in real concrete structures is evaluated by focusing on the fatigue performance of GFRP RC members. A fatigue test was conducted on concrete decks reinforced with the GFRP rebar. Eight full-scale decks were constructed and tested in the laboratory. The test parameters were rebar type, reinforcement ratio in the bottom transverse direction, and cyclic load magnitude. It was observed that a GFRP reinforced concrete deck on restrained girders behaves similarly to a steel reinforced concrete deck, except for deflection behavior. Also, the study results showed that the GFRP RC deck was strongly affected by the magnitude of the applied cyclic load. Also, the test result showed that a load of 58% less than or equal to the maximum static load carrying capacity should be applied to the deck to safely carry a load of two million cycles. The GFRP RC deck on restrained girders showed reasonably good fatigue resistant capacity. Copyright © 2015 Japan Concrete Institute.

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